Manometric accelerometer



Dec. 15, 1953 R. E. BAREFORD MANOMETRIC ACCELEROMETER Filed May 5, 1952 iratented Dec. 15, 1953 A UNITE-o s'rAre narrar ofi-Fica MAN OMETRIC ACCELEROMETER Robert E. Bareford, Burbank, Ga1if;, assignor to' N orthrop.- Aircraft, Inc.,

Hawthorne,. Calif., a

corporation of California ApplicationMay 3, 1952, S'crialNo; 285,961

8- Claims.

Tnet-present;invention relates a device for' indicating acceleration and attitudeoi a bcdyfon' ments citen containing a body oi mercury movement of which completed contacts in the electricalcircuit ofthe instrument and effected the operation of ari-indicating instrument.

A common fault of known types of aeeel etersiandf levels isI the erratic eA cracter el? readings given byythe instrument aus to lack ci control ioi, the Amercurycr liquid;

It is the general object of my invention to provide anzinstrument'ior indicating aeceleration, deceleration'orangles-oftiltzoi arb V on which itr is mounted; thel readings v ofy the inet-ruin beingrmore linear, owinginrpartto control exercised? onv the movement of liduid'in the device., than' those aiordedr by other instruments.

Another objectci invention is to provide anxinstrument of the type deseribedwhich will operate over `a greaterrange of movement knowninstruments ofthe saine general type.

A still further object of my invention vis to provide an aecelerometer` and; level indicator of simple and, strong construction providing accuratexreadings:

Yeti another object .of my invention is to provideeassensitive and accurateinstrurnent for the purpose desermedv-Jh'iclris freeV from deterioration ;in use;

Allstill further objectl of invention to provide'. an instrument in which the parts are permanently sealed in place thus avoiding the risk of faulty functioning dueto parte working loose;

With: the above and-*other objects in View the invention comprises an acceleroineter and level indicating instrumentl having a bodyof insulating materiallprovided With chambers mounted vertically in spaced relation, the chambers being connectedwat their lower-ends by a conduit and having'electrodes projectingr into the chambers` andrinto an. electrolyte lling the flower ends of the chambers and said conduit. are connected in a suitable bridge circuit and the value of acceleration or deceleration or angle of tilt is efective to produce a signal which may be indicated by an-inetrument in the circuit.

Still` further features and advantages oi the invention will hereinafter appear from the fol- Thel electrodes f 2. lowing; spe'oication'read with reference to theaccompan'ying' drawings which illustrate anembodimenty of the invention at present thought preferable to me.

in' the drawings:

Figurey 1fis' a central vertical sectionthroughf the devicey of the4 invention.

FigureZis a crosssection on the line 2e-Eloi Figure 1, draivnon'a smaller scale.

Figure 3 is schematic diagramY showing' the instrument connecte-:lin a suitable bridge circuit, electrodes being* shown `for clarity: spaced -in i the longitudinal plane of the instrumentv although this is notr their actual arrangement' Figure 4. isa graph shoivingreadings*obtained from the device` When-usadas a leyel andfshowthe linearity of the readings.

In Figure 1 the numeral i genera-ily indicates. tliedevice, comprise,` a irsttubular member a base Section tr and a second tubular member 3, all parts ofthe instrument exceptA those includedin'an electrical circuit later describe-cl, being formed cinch-conductive'material.

The tubular membersrform. identical chambers and E; respectively spaced f apart ori-the base The' member and' connected :y a1 con-fluit 6; lower portions of the chambers 4 and 5 and oonduit Stare iilled with a suitableliquidi.

rI'he desirable characteristias Vor the liquid used include electrical stability under Variation-sof temp'erature,v a suitable liquid:ii/as foundto be' a .02 molar concentration-or" magnesium nitrate using ethanol as a solvent; theiormula beingk 'Ihe'form` of the: conduit fis of particular importancesince it' controls the o'w ofliquid fromV one chamber to the other consequent on a difference of'level therein due to a tilt of the instrument or a sudden change in the rate of movement' of a vehicle on which the instrument is carried.-

In Figure 1 the conduit isvshown, by Way of" example, ivith a ,restricted-throat 8- and identically` flared-sections?! connectingthe throaty to .the tubular chambers# and-Efit has been found in practice-that an angle of are of about 15 'provides'a-smooth now of liquid-.through the conduit'- 6:

The vdiameter of the throat' is'determined byv the desired degree of damping of the oW of liquid, and the throat or portion of minimum diameter. of i the conduit E-rnay be positioned" Wh'ere-frequired, for instance the bestpositionsl and 5, this arrangement however increases the height of the instrument.

rod, preferably including iridium to increase its mechanical strength, and since the upper ends of the electrodes are sealed into the cap portion forming the top of the chambers, which are conveniently made of glass, the upper end I2b is formed of a tungsten rod electrically welded at E to the lower end 12a. The upper end I2b is fitted into and welded to a glass sleeve I2cl which projects over the welded junction I2C to protect the tungsten from the electrolyte, the sleeve in turn being welded to the cap portion of the chamber. To facilitate attachment of leads to the electrodes lug I2e is soldered to the upper end of rod |217. It should be noted that the platinum end of the electrodes are immersed to an equal extent in the liquid in the chambers while the instrument remains level or is being moved in the direction of its longitudinal axis at a constant speed.

In order to equalize the pressure in the upper part of the chambers 4 and 5, a conduit I6 is provided in the cap portion to extend between them. The conduit I6 is also used, when producing the device, to introduce the liquid therein, a short neck l1 being provided for this purpose, the neck thereafter being sealed ofi as indicated in Figure 1. Preferably the conduit is sloped downward from the mid-point of its length in order to facilitate drainage of any liquid therefrom that may enter the passage due to violent movement of the vehicle on which it is carried, this slope may be about 15.

The device is advantageously made entirely of Pyrex glass, the various parts being molded or cast to specification and fused together as indicated by the dotted joint lines in Figure 1.

The instrument is incorporated in preferably an A. C. Wheatstone resistance bridge circuit as shown in Figure 3, in which the secondary of a transformer is indicated at I8 which may be used to supply 2.5 volts at 400 c. p. s. to the legs ofthe circuit. The electrodes I2 and I3 in chamber Vl of the device of my invention are connected in one leg of the circuit, and the electrodes IB, I5 in chamber 5 are connected in the opposite leg of the bridge.

The midpoint of a connection between electrodes IS and I5 is connected through a vacuum tube voltmeter (V. T. ,V. M.) to helipot H which is connected between the arms of the bridge circuit and is the equivalent after initial adjustment of the usual matched resistances.

The functioning of the instrument of my invention is dependent on the variation of resistance in the arms of the bridge circuit by the extent of immersion of the electrodes in one chamber as compared with the immersion of the electrodes in the other chamber.

While the instrument remains level the electrodes in both chambers will be immersed to an equal extent in the liquid in the chambers and therefore the resistance in the arms of the Wheatstone bridge circuit will balance and no reading will bershown by the voltmeter (V. T. V. M.). If the device is tilted in its vertical plane the level of the liquid will of course rise in one chamber and fall in the other chamber thus unbalancing the bridge circuit andvgiving a reading on the scale of the voltmeter.

Figure 4 is a graph of a test on the instrument when used as a level, seconds of arc of tilt being plotted against linear deviations of voltage. It will be noted that the deviations from linear are very small and the instrument gives Va much better reading than obtainable from known instruments of the same general type.

When the instrument is used to measure acceleration or deceleration in the direction of its longitudinal axis the inertia of the liquid will cause flow from the leading chamber to the other thus causing unbalance of the Wheatstone bridge. The imbalance of the bridge circuit could of course be utilized to afford a signal controlling corrective mechanisms of any suitable type ifV required.

The sensitivity of the instrument is shown by the fact that under test it was determined that an angle of tilt as small as one second of arc was detected while the range of the instrument as constructed exten-ded to 14. The range oi' the instrument obviously will depend on the depth to which the electrodes are immersed in the electrolyte in the horizontal position of the instrument.

When used as an accelerometer, the instrument illustrated was found to detect an acceleration of .0005070 of 1g(K) while the range extended to 25% of 1g(K)".

The outstanding features of the instrument of my invention as proved by test are linearity,

sensitivity, and stability achieved by a structure of simple design.

While in order to comply with the statute, the invention has been described in language more or less specic as to structural features, it is to be understood that the invention is not limited tc the specific features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modiiications within the legitimate and valid scope of the appended claims.

What I claim is:

l. An electrically operated instrument for indicating acceleration and attitude, including: chambers formed of insulating material and spaced from one another in a horizontal plane; conduit means connecting the lower portions of said chambers, said conduit means adapted to be lled and said chambers to be partly lled with electrolyte; and separate electrode means rigidly mounted in said chambers and projecting into the electrolyte when placed in the instrument in each chamber to an extent dependent on the vertical displacement of the electrolyte in the chambers so that the resistance or an electric path including said electrode means and electrolyte is varied by the extent to whichthe electrode means are immersed in the electrolyte.

2. An electrically operated instrument for indicating acceleration and attitude,v including: chambers formed of insulating material spaced from one another in a'horizontal plane; conduit means connecting the lower portions of saidY chambers, said conduit means adapted to be filled and said chambers to be partly filled with electrolyte; separate electrode means rigidly mounted in said chambers and projecting into the electrolyte when placed in the instrument in each chamber to an extent dependent on the vertical displacement of the electrolyte in .the

chambers so that the resistance of an electric path including said electrode means and electrolyte is varied by the extent to which the electrode means are immersed in the electrolyte; a cap portion of insulating material closing the upper ends of said chambers; and conduit means connecting the upper ends of said chambers.

3. An electrically operated instrument for indicating acceleration and attitude including: identical tubular chambers of insulating material projecting upwardly from a base member and spaced apart thereon; conduit means connecting the lower portions of said chambers, said conduit means adapted to be filled and said chambers to be partly lled with electrolyte; a cap portion of insulating material closing the upper ends of said chambers; separate electrode means rigidly mounted in the cap member and projecting downwardly into said electrolyte in each chamber to an extent dependent on the vertical displacement of the electrolyte in the chambers so that the resistance of an electric path including said electrode means and electrolyte is varied by the extent to which the electrode means are immersed in the electrolyte; and a passage through said cap portion connecting the upper ends of said chambers.

4. An electrically operated instrument for indicating acceleration and attitude, including: tubular chambers of insulating material projecting upwardly from a base portion of insulating material and spaced apart thereon; a conduit connecting the lower portions of said chambers, said conduit adapted to be lled and said chambers to be partly lled with electrolyte, said conduit having a restricted portion to provide a predetermined damping of the flow of liquid at times from one chamber to the other; and separate electrode means rigidly mounted in said chambers and projecting into the electrolyte when placed in the instrument in each chamber to an extent dependent on the vertical displacement of the electrolyte in the chambers so that the resistance of an electric path including said electrode means and electrolyte is varied by the extent to which the electrode means are immersed in the electrolyte.

5. An electrically operated instrument as set forth in claim 4 and in which the restricted portion of the bore of said conduit is connected by sloped portions to the bore of said tubular chambers to provide a smooth flow of the electrolyte through the conduit, the angle of said sloped conduit portions being less than about 15.

6. An electrically operated instrument for indicating acceleration and attitude, including: tubular chambers of insulating material projecting upwardly from a base portion of insulating material and spaced apart thereon; a conduit connecting the lower portions of said chambers; an electrolyte filling said conduit and partly filling the chambers; a plurality of spaced electrode means rigidly mounted on each chamber and projecting into the electrolyte therein; a cap portion of insulating material closing the upper ends of said chambers; and a passage through said cap portion connecting the upper ends of said chambers.

7. An instrument as set forth in claim 6 and in which each of said electrodes comprises an upper portion, a sleeve enclosing said upper portion and formed from a material resistant to and protecting the upper portion of the electrode from the electrolyte, and a lower electrode portion of chemically inert material.

8. An instrument as set forth in claim 6 and in which said passage in the cap is sloped downwardly from a central portion and is initially provided with a lling neck at that portion for the introduction of electrolyte said neck being subsequently sealed.

ROBERT E. BAREFORD.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Name Date 1,317,072 Carlier Sept. 23, 1919 2,067,467 Urfer Jan. 12, 1937 

